Sidhartha Chaudhury

Peacekeeping operations in sub-Saharan Africa continue to be impacted by malaria both in-country and among returning service members. The Royal Thai Army (RTA) deploys an engineering company to Juba and Rumbek, South Sudan to conduct peacekeeping operations as part of the UN Mission in South Sudan (UNMISS). Each deployment is approximately 12 months long. The unit is given doxycycline one week before travel before switching to the UN-provided mefloquine during deployment and for four weeks after returning. The RTA routinely conducts post-deployment screening for malaria by microscopy and PCR for units returning from UNMISS. High rates of prophylaxis failure were observed from both during-mission and post-deployment screening cases, with cumulative malaria attack rates of 11.4% (31 cases out of 271 personnel), 18.2% (49 cases out of 270 personnel), and 23.1% (63 cases out of 273 personnel) for 2023, 2024, and 2025, respectively, with 98% of cases being due to P. falciparum. Furthermore, post-deployment screening revealed high rates of sub-microscopic and sub-clinical parasitemia with 40% of all malaria cases being identified as asymptomatic during post-deployment screening, and 61% of those asymptomatic cases being detected by PCR only. While factors underlying the high prophylaxis failure rate, as well as the high rate of sub-microscopic and sub-clinical parasitemia are unclear, these findings highlight the limitations of relying on clinical symptoms or microscopy for detecting malaria in military units returning from endemic regions and underscore the importance of unit-wide post-deployment molecular screening.

While vector control methods have successfully reduced malaria rates worldwide, such methods are not always suitable for military use. We evaluated the usability, durability, and effectiveness of permethrin-treated uniforms and metofluthrin spatial repellent in preventing mosquito bites among soldiers in the Laos People’s Army that were deployed on a 12-week field exercise. The study enrolled 173 subjects into four different groups: (1) metofluthrin-only, (2) permethrin-treated uniforms, (3) metofluthrin with permethrin-treated uniforms, and (4) a control group. We measured efficacy through self-reported survey responses and a serological test for antibodies to Anopheles salivary antigens and assessed the durability of permethrin treatment over the 12-week exercise. We found that soldiers given metofluthrin and permethrin-treated uniforms were 72% and 46% more likely to report decreased mosquito bites compared to those in the control group and that soldiers with permethrin-treated uniforms had significantly lower (p < 0.05) antibody levels to the Anopheles SG6 salivary antigen. Mass spectrometry analysis revealed that treated uniforms still contained a significant permethrin concentration that showed 50 to 100% mosquito mortality. Overall, our findings show that both metofluthrin and permethrin-treated uniforms were well-tolerated and led to significantly fewer reported mosquito bites, and that permethrin, in particular, was found to be durable throughout the 12-week field exercise and effective in reducing mosquito bite exposure, underscoring its value in military applications.

The Indo-Pacific region hosts several annual military exercises that involve the deployment of thousands of U.S. and partner-nation military personnel. Respiratory and diarrheal diseases pose a significant health risk to exercise participants and represent a substantial portion of medical encounters and lost duty days. We conducted surveillance for respiratory and diarrheal illness at the Cobra Gold and Balikatan military exercises in Thailand and the Philippines from 2023–2025. Through coordination with health providers in the field, military personnel that reported acute symptoms were asked to provide a nasopharyngeal swab or stool sample. These samples were transported to a field lab and tested by PCR for common respiratory and diarrheal pathogens. Follow-up analyses included bacterial culture, antimicrobial susceptibility testing, and viral whole-genome sequencing. From 84 respiratory and 61 diarrheal samples analyzed, we found that respiratory illness was primarily attributed to rhinoviruses/enteroviruses (23%), common coronaviruses (21%), and SARS-CoV-2 (11%) while diarrheal disease was attributed to a high rate of diarrheagenic E. coli (73%) and norovirus (20%), followed by Salmonella spp. (18%) and Campylobacter spp. (13%). Our findings highlight the distinct etiologies of respiratory and diarrheal disease in military field settings and demonstrate the feasibility of conducting real-time infectious disease surveillance in operational environments.

Background: Identifying effective malaria elimination strategies for remote regions and highly mobile populations in Southeast Asia is challenging given limited resources. In this clinical trial, two malaria elimination strategies were evaluated in partnership with the Royal Cambodian Armed Forces - monthly malaria prophylaxis (MMP) and focused screening and treatment (FSAT). Methods: Eight military cohorts (1,050 volunteers total) along the Cambodian-Thai border were randomly assigned to three months of either MMP or FSAT (four cohorts in each treatment arm) with monthly malaria testing for six months. Cohorts were further randomly assigned to receive either permethrin treated (ITU) or sham-treated clothing (sITU). Volunteers in MMP cohort were given three monthly three-day doses dihydroartemisinin-piperaquine (DP) along with a ‘universal’ low-dose weekly regimen of 22.5 mg primaquine for 12 weeks, intended for use regardless of body weight or G6PD status. Volunteers in FSAT cohort were treated with appropriate first-line antimalarials if they tested positive for malaria. Results: Plasmodium falciparum ( Pf ) positivity in MMP cohorts was reduced by 90% (10% at enrollment to 1% at six months; absolute risk reduction (ARR) 9%) at 6 months. However, 32% of Pf cases treated with DP as MMP at baseline recrudesced, requiring rescue treatment at 1 month with artesunate-mefloquine. Pf positivity in FSAT cohorts declined 66% over six months (7.6% to 2.7%; ARR 4.9%). MMP reduced P. vivax ( Pv ) positivity from 9% to 0% at three months, but Pv rebounded to 6.7% at six months. FSAT failed to significantly reduce Pv positivity during the study. The 22.5 mg weekly primaquine MMP regimen was safe, even for the 15% of volunteers with G6PD-deficiency. Those wearing ITU had additional Pv parasitemia reductions compared to sITU in the FSAT but not MMP cohorts. Conclusions: MMP was safe, and superior to FSAT, suggesting greater utility to achieve malaria elimination in Cambodia. Low dose (22.5 mg) weekly primaquine was a safe adjunct in this setting, even for those with G6PD-deficiency. Permethrin-treated clothing further reduced Pv parasitemia for FSAT but not MMP. We observed that MMP may be more easily scaled to eliminate malaria and that the military may provide substantial support for regional elimination efforts. Trial registration: The study was registered on https://clinicaltrials.gov/ on 13-01-2016 prior to enrollment (NCT02653898).

Staphylococcus aureus (S. aureus), especially methicillin-resistant S. aureus (MRSA), remains a major public health concern. This study reports the antimicrobial resistance profiles and molecular characteristics of 31 S. aureus isolated during 2017–2018 from inpatient and outpatient clinical specimens from Queen Sirikit Naval Hospital (QSH) in Chonburi province, Thailand. All isolates were tested for antimicrobial susceptibility. Staphylococcal cassette chromosome mec (SCCmec) typing, Panton–Valentine leukocidin (pvl) toxin, pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), and staphylococcal protein A (spa) typing were performed. Twenty-seven isolates were confirmed to be MRSA and exhibited resistance to up to seven antibiotics classes. The main MLST type was SCCmec type II (51.9%) and ST764 (55.6%). Five spa types were identified with t045 (55.6%) as the major type. All 31 S. aureus isolates were grouped into seven types using PFGE with the SCCmecII-ST764-t045 clone being the most prevalent. Overall, our findings reveal that the S. aureus isolates in this study differ from previous reports in Thailand, indicating a potential shift in local strains, highlighting the need for ongoing molecular surveillance of multidrug resistance patterns of MRSA in Southeast Asia.

Reproducibly assessing malaria exposure is critical for force health protection for military service members deployed to malaria-endemic regions as well as for civilians making public health decisions and evaluating malaria eradication efforts. However, malaria disease surveillance is challenged by under-reporting, natural immunity, and chemoprophylaxis, which can mask malaria exposure and lead to an underestimation of malaria prevalence. In this study, we determined the feasibility of using a serosurveillance-based approach to measure Anopheles vector exposure, Plasmodium sporozoite exposure, and blood-stage parasitemia using a multiplex serological panel. We tested post-deployment samples obtained from U.S. service members returning from regions with malaria risk to assess the potential of this serosurveillance panel. The results identified that some service members had anti-CSP antibody levels comparable to those found in endemic populations, suggesting exposure to sporozoites while those individuals were on chemoprophylaxis. We also observed isolated cases of anti-MSP1 levels that were as high as those observed in endemic populations and in CHMI studies, suggesting possible cases of clinical or subclinical parasitemia. The study demonstrated the feasibility of implementing a multiplex serology approach for conducting serosurveillance for Anopheles vector exposure and Plasmodium parasite exposure in samples collected following military deployments and its potential to support public health policies.

Background: Identifying effective malaria elimination strategies for remote forested regions in Southeast Asia is challenging given limited resources. In this study, two malaria elimination strategies were evaluated in partnership with the Royal Cambodian Armed Forces - monthly malaria prophylaxis (MMP) and focused screening and treatment (FSAT). Methods: Eight primarily military clusters (1,050 volunteers total) along the Cambodian-Thai border were randomized to 3 months of MMP or FSAT with monthly malaria testing by RDT, PCR, and microscopy for six months. Clusters were sub-randomized to permethrin treated (ITU) or sham water-treated clothing (sITU). Volunteers in MMP clusters were given three full monthly dihydroartemisinin-piperaquine (DP) treatment courses with 12 weekly 22.5mg primaquine. Volunteers in FSAT clusters were treated with appropriate first-line antimalarials if malaria-positive by microscopy or PCR. Results: Pf positivity in MMP clusters was reduced by 90% (10% at enrollment to 1% at 6 months; absolute risk reduction (ARR) 9%) at 6 months. However, 32% of Pf cases treated with DP as MMP at baseline recrudesced, requiring rescue treatment at 1 month with artesunate-mefloquine. Pf positivity in FSAT clusters declined 66% over 6 months (7.6% to 2.7%; ARR 4.9%). MMP reduced Pv positivity from 9% to 0% at 3 months, but Pv rebounded to 6.7% at 6 months. FSAT failed to significantly reduce Pv positivity during the study. The 22.5mg weekly primaquine MMP regimen was safe, even for the 15% of volunteers with G6PD-deficiency. Those wearing ITU had additional Pv parasitemia reductions compared to sITU in the FSAT but not MMP groups. PCR was more sensitive than microscopy and RDT for detecting both species. Conclusions: MMP was safe, and superior to FSAT to reduce Pf and Pv , suggesting greater utility to achieve malaria elimination in Cambodia. Low dose (22.5mg) weekly primaquine was a safe adjunct in this setting, even for those with G6PD-deficiency. Permethrin-treated clothing further reduced Pv parasitemia for FSAT but not MMP. MMP may be more easily scaled to eliminate malaria. The military may provide substantial support for regional elimination efforts.

Objective: To describe the profile and specificity of maternal and neonatal cord-blood antibody profile in response SARS-CoV-2 virus exposure Methods: This is a Prospective cohort study of delivering patients at Thomas Jefferson University Hospital from April 2020-February 2021. Primary objective was to describe unique maternal and fetal antibody epitope titers and specificity in those patients with COVID-19 history. Serologic profile assessed with a multiplex platform. Antigens used were: HA-trimer Influenza A (Hong Kong H3), spike trimers for SARS-CoV-2, SARS-CoV-1, MERS-CoV, and betacoronaviruses HKU-1 and OC43, as well as the spike N-terminal domain (NTD), spike receptor binding domain (RBD), and nucleocapsid protein (N; full length) for SARS-CoV-2. Results: 112 maternal samples and 101 maternal and cord blood pairs were analyzed. Thirty-seven had a known history of COVID-19 (positive PCR test) in the pregnancy and of those, 17 (47%) were diagnosed with COVID-19 within 30 days of delivery. Fifteen of remaining seventy-six (20%) without a known diagnosis had positive maternal serology. For those with history of COVID-19 we identified robust IgG response in maternal blood to CoV2 nucleocapsid (N), spike (S) full-length and S (RBD) antigens with more modest responses to the S (NTD) antigen. By contrast, the maternal blood IgM response appeared more specific to S (full-length), than N, S (RBD) or S (NTD) epitopes. There were significantly higher maternal and cord blood IgG response not just to CoV2 spike (p < 10 ⁻¹⁸ ), but also CoV1 spike (p < 10 ⁻⁹ ) and MERS spike (p < 10 ⁻⁸ ). By contrast, maternal IgM responses were more specific to CoV2 (p < 10 ⁻¹⁹ ), but to a lesser degree for CoV1 (p < 10 ⁻⁵ ), and no significant differences for MERS. Maternal and cord-blood IgG were highly correlated for both S and N (R ² = 0.96 and 0.94). Conclusions: Placental transfer is efficient, with robust N and S responses. Both nucleocapsid and spike antibody responses should be studied for a better understanding of COVID-19 immunity. IgG antibodies are cross reactive with related CoV-1 and MERS spike epitopes while IgM, which cannot cross placenta to provide neonatal passive immunity, is more SARS CoV-2 specific. Neonatal cord blood may have significantly different fine-specificity than maternal blood, despite the high efficiency of IgG transfer.

Serological assessment of SARS-CoV-2 specific responses are an essential tool for determining the prevalence of past SARS-CoV-2 infections in the population especially when testing occurs after symptoms have developed and limited contact tracing is in place. The goal of our study was to test a new 10-plex electro-chemiluminescence-based assay to measure IgM and IgG responses to the spike proteins from multiple human coronaviruses including SARS-CoV-2, assess the epitope specificity of the SARS-CoV-2 antibody response against full-length spike protein, receptor-binding domain and N-terminal domain of the spike protein, and the nucleocapsid protein. We carried out the assay on samples collected from three sample groups: subjects diagnosed with COVID-19 from the U.S. Army hospital at Camp Humphreys in Pyeongtaek, South Korea; healthcare administrators from the same hospital but with no reported diagnosis of COVID-19; and pre-pandemic samples. We found that the new CoV-specific multiplex assay was highly sensitive allowing plasma samples to be diluted 1:30,000 with a robust signal. The reactivity of IgG responses to SARS-CoV-2 nucleocapsid protein and IgM responses to SARS-CoV-2 spike protein could distinguish COVID-19 samples from non-COVID-19 and pre-pandemic samples. The data from the three sample groups also revealed a unique pattern of cross-reactivity between SARS-CoV-2 and SARS-CoV-1, MERS-CoV, and seasonal coronaviruses HKU1 and OC43. Our findings show that the CoV-2 IgM response is highly specific while the CoV-2 IgG response is more cross-reactive across a range of human CoVs and also showed that IgM and IgG responses show distinct patterns of epitope specificity. In summary, this multiplex assay was able to distinguish samples by COVID-19 status and characterize distinct trends in terms of cross-reactivity and fine-specificity in antibody responses, underscoring its potential value in diagnostic or serosurveillance efforts.